Conventionally, in some cases, a moving object moving on a plane such as a road is imaged at a predetermined depression angle, by a camera set above the plane. An image processing device is sometimes used to recognize a specific pattern of the moving object within an image picked up by the camera, thereby obtaining information of the pattern. In this image recognition, it is important that the moving object on the image is clear to make it possible to sufficiently obtain information of the pattern.
A technique can be used to enable to automatically focus a camera onto a moving object. For example, a technique is known that enables to image a moving object at plural times each time the moving object passes within an imaging range, and estimate a motion of the moving object based on a change of an out-of-focus level of the moving object within each image, thereby adjusting the focus onto the moving object (see Japanese Laid-open Patent Publication No. 07-92381).
However, in the conventional technique described above, a lens is focused onto the moving object each time. Therefore, the focus is sometimes deviated far from the moving object because of a wrong estimation. In such cases, the camera cannot be focused onto the moving object.